1. Field of the Invention
The present invention generally relates to the field of navigation and/or position tracking. In particular, the present disclosure is directed to a personal navigation system that uses foot-mounted inertial sensors and associated methods.
2. Description of the Related Art
Personal navigation and tracking systems are being developed today for use in any number of applications. In one example, personal navigation and tracking systems may be useful in military applications for tracking and directing the movements of military personnel during military practice maneuvers and/or military battlefield environments. In another example, personal navigation and tracking systems may be useful in field service applications for tracking field service personnel and/or a fleet of vehicles that have been dispatched into the field. In yet another example, personal navigation and tracking systems may be useful in first responder applications for tracking and directing the positions of, for example, law enforcement personnel at the scene of a crime or accident, firefighters at the scene of an accident or fire, and/or emergency medical services (EMS) personal at the scene of an accident.
With respect to first responder applications, firefighters have lost their lives because of the lack of effective indoor navigation and tracking systems. As a result, there is particular interest in developing effective navigation and tracking systems for indoor use. While navigation and tracking systems for outdoor use have been effectively implemented using, for example, satellite-based navigation systems, such as Global Positioning System (GPS) technology, traditional systems for navigating indoors, such as within a building, are generally costly or ineffective. For example, the installation and operating costs associated with an installed base of radio frequency markers within a building are substantial barriers not readily overcome. In addition, poor reception of radio frequency navigation signals within a building, such as that used by satellite-based navigation systems, precludes widespread acceptance.
More specifically, indoor environments pose particular challenges with respect to implementing navigation and tracking systems. For example, signal transmission in indoor environments may be characterized by the presence of reflections, attenuation, low signal to noise ratio, and signal multipath effects; all of which may decrease tracking accuracy and may prevent signal acquisition all together. Further, multiple story buildings pose additional obstacles for tracking, as they require three-dimensional positioning.
Another type of navigating system is an inertial navigation system (INS), which is a navigation aid that uses a computer and motion sensors to continuously calculate via dead reckoning the position, orientation, and velocity of a moving object without the need for external references.
An INS includes at least a computer and a platform or module containing accelerometers, gyroscopes, or other motion-sensing devices. A typical INS is initially provided with its position and velocity from another source (a human operator, a GPS satellite receiver, etc.), and thereafter computes its own updated position and velocity by integrating information received from the motion sensors. The advantage of an INS is that it requires no external references in order to determine its position, orientation, or velocity once it has been initialized.
Inertial navigation systems are used in many different moving objects, including vehicles, aircraft, submarines, spacecraft, and guided missiles. However, their components size, cost, and complexity places constraints on the environments in which INS is practical for use.
A further shortcoming of inertial navigation systems is that they suffer from “integration drift.” For example, small errors in the measurement of acceleration and angular velocity are integrated into progressively larger errors in velocity, which is compounded into still greater errors in position. This is a problem that is inherent in every open loop control system. Since the new position is calculated solely from the previous position, these errors are cumulative, increasing at a rate roughly proportional to the time since the initial position was input. Therefore the position fix must be periodically corrected by input from some other type of navigation system. The inaccuracy of a good-quality navigational system may be as much as 0.6 nautical miles per hour in position and on the order of tenths of a degree per hour in orientation.
In view of the shortcomings of the aforementioned navigation and tracking systems, a need exists for new approaches to personal navigation and tracking. In particular, a need exists for a practical and cost-effective personal navigation and tracking system that is highly accurate and reliable in any environment and that is suitable for use in any application, such as, but not limited to, military applications and first responder applications.